The present invention relates to a spur-gear system of the kind having an outer gear-wheel adapted to be rigidly connected to a component which is to be driven, said outer gear-wheel being mounted, via a common self-aligning bearing disposed at least approximately concentrically within the outer gear-wheel, on a support, and a pinion gear-wheel which meshes with the outer gear-wheel also mounted on the support via a self-aligning bearing disposed concentrically within the gear-wheel.
Such a spur-gear system is especially suitable for driving a hollow roll shell rotating round a stationary inner part. Such rolls are, for example, flexion adjusting rolls or suction rolls, such as those used in the paper industry in dewatering presses, calenders or the like. A particularly appropriate application for the invention is for the so-called equidistantly mounted flexion adjusting rolls where the bearings of the roll shell, the bearings of the mating roll and the spheroidal mountings for the yoke (the flexion support extending through the roll shell) are disposed with at least approximately the same distance between them.
A spur-gear system of the above kind is known from German laid-open Patent Specification (DE-OS) No. 30 24575, FIG. 3, which correponds substantially to U.S. Pat. No. 4,414,890. In the prior art system, the outer gear-wheel of the spur-gear system is rigidly connected to the roll shell. Disposed concentrically inside the outer gear-wheel there is a self-aligning bearing; that is the center point of the self-aligning bearing lies at least approximately in the central plane of the outer gear-wheel, this plane extending perpendicular to the axis of rotation of the roll. A pinion gear-wheel which meshes with the outer gear wheel is mounted in a similar way. This gearing system, which is extremely simple in comparison with other known designs, enables the two gear-wheels to adjust to a certain extent into an inclined position during operation. A position which is inclined at a relatively small angle may arise, for example, if the roll shell flexes during operation. A position which is inclined at a relatively large angle arises if the entire roll, when either idling or stopped, is swung out of a rest position into an operating position or back again. In the latter case, it must be borne in mind that the pivot levers do not generally move exactly synchronously.
The above publications thus disclose a development step in the right direction. However, it has subsequently been realized that the pinion gear-wheel could swing perpendicular to the engagement plane of the teeth during operation. That is to say, it could incline by a small angular amount out of the normal position in which the axes and tooth flanks of the two gear-wheels lie parallel to each other. As soon as the pinion gear-wheel inclines, contact between the teeth will occur only in a narrow area in the center of the gear-wheels, so that there is a danger of over-loading at that location. The inclining or swinging of the pinion gear-wheel will occur whenever there is an asymmetrical load, for example, due to any alignment error between the roll shell and the drive shaft.
The object of the present invention is to improve the gear system described in DE-OS No. 30 24 575 so that the axes of the two gear-wheels remain parallel during normal operation.